Re: Elaboration worries

[Robert A Duff <bobduff@shell01.TheWorld.com>]

"Alex R. Mosteo" <devnull@mailinator.com> writes:

> a) make your package Pure.
> b) if not possible, make it Preelaborate.
> c) if not possible, put an Elaborate_Body in the spec.
> 
> I was happy following this rule, but just recently I've started to
> experiment with the -gnatwl switch, that warns when a "Elaborate_All" is
> needed. I have two questions related with this. 
> 
> The first one is that I don't really grasp why a "Elaborate_All" could be
> needed if one strictly follows the tree rules above.

I don't think you can follow those three rules in all cases,
because they place restrictions on the code you can write.
For example, Elab_Body prevents a package body from with-ing
its children.

There's a good description of elab issues in the GNAT docs.

> The second one is this: by my observation of the gnat warnings, it seems
> that the requirement for "Elaborate_All" is a "server side" one. However, I
> must use the E_A in all "client side" units. This is because contrarily to
> the abc) rule pragmas, that can refer to the package where they appear, E_A
> can not.

Yes, that is a pain.

> Example: Package A causes a warning for E_A in all packages that use
> A.


No -- only if they use A at elaboration time.

>... I
> can't do nothing at A to remove the warning, but to put an E_A(A) in all
> client packages. This seems strange to me.

Yes, it is strange.

> A final note is that this second situation happens to me mostly with generic
> units.

Yes, that's because generic instantiations are usually at library level,
and are therefore elaborated at library package elab time.

- Bob